The present invention relates to a novel titanyl phthalocyanine crystal formed from a titanyl phthalocyanine compound. The present invention also relates to a method of producing the titanyl phthalocyanine crystal. The present invention also relates to an electrophotosensitive material using the titanyl phthalocyanine crystal as an electric charge generating material.
Electrophotosensitive materials are used in image forming apparatuses such as electrostatic copying machine, laser printer and plain paper facsimile.
As the electrophotosensitive material, a so-called organic photosensitive material formed by using the following components in combination has widely been used.
Electric charge generating material which are irradiated with light to generate electric charges (holes and electrons)
Electric charge transferring material for transferring the generated electric charges, which is classified into a hole transferring material for transferring holes and an electron transferring material for transferring electrons.
Binding resin having a film forming property.
The organic photosensitive material has such an advantage that it is easily produced as compared with an inorganic photosensitive material using an inorganic semiconductor material.
The organic photosensitive material also has advantages such as wide range of choice of materials such as electric charge generating material, electric charge transferring material and binding resin, and high functional design freedom.
The organic photosensitive material is produced by forming a single-layer or multi-layer type photosensitive material on a conductive substrate.
The single-layer type photosensitive layer contains an electric charge generating material, an electric charge transferring material (hole transferring material and/or electron transferring material) and a binding resin in the same layer.
The multi-layer type photosensitive layer is formed by mutually laminating at least two layers among an electric charge generating layer containing an electric charge generating material, an electric charge transferring layer containing an electric charge transferring material (hole transferring material and/or electron transferring material), and a photoconductive layer containing an electric charge generating material and at least one of a hole transferring material and an electron transferring material.
As the electric charge generating material, for example, various pigments can be used according to the sensitivity range of the photosensitive material.
As the electric charge generating material for photosensitive material which is sensitive to infrared or near infrared light emitted from a semiconductor laser or infrared LED, for example, phthalocyanine pigments have widely been used.
The phthalocyanine pigment varies depending on the chemical structure and includes, for example, metal-free phthalocyanine compound, copper phthalocyanine and titanyl phthalocyanine. The respective compounds can be in various crystal forms.
Therefore, crystals having various crystal forms of various phthalocyanine compounds have been studied by a lot of investigators to find out optimum crystals suited best for use as the electric charge generating material.
For example, Japanese Patent Publication No. 2907121 discloses that a crystal having a Y type crystal form of titanyl phthalocyanine is superior in sensitivity characteristics for electric charge generating material to a crystal having the other crystal form and can contribute to an improvement in sensitivity of the electrophotosensitive material.
A coating solution for the single-layer type photosensitive layer, or a coating solution for electric charge generating layer of the multi-layer type photosensitive layer using the Y type titanyl phthalocyanine crystal can be prepared by adding the crystal and other components in an organic solvent and uniformly dispersing them.
The layer formed by coating the coating solution on the substrate immediately after preparation or within about 60 minutes, and drying the coating solution is particularly superior in sensitivity characteristics as described in the above publication.
However, the sensitivity characteristics of the layer, which was formed by coating the coating solution after storage for a fixed time (e.g. 24 hours) and drying the coating solution, is drastically lowered as compared with the layer formed by using the coating solution immediately after preparation.
It has been found that, since the coating solution prepared by using the Y type titanyl phthalocyanine crystal described in the above publication is inferior in storage stability, the photosensitive layer having good sensitivity characteristics can not be formed stably.
Japanese Laid Opened Patent Application No. 2001-181531 (2001) proposed a titanyl phthalocyanine crystal which gives a coating solution capable of forming an electrophotosensitive material having good sensitivity characteristics even when stored for 24 hours after the preparation of the coating solution, and an electrophotosensitive material using the same.
However, the present inventors have studied and found that the storage stability of the coating solution is insufficient in stable storage only for 24 hours and it is necessary to further improve the storage stability.
As a coating apparatus for producing an electrophotosensitive material by applying a coating solution on a substrate, there is generally used a circulating type coating apparatus wherein the coating solution, which was not deposited on the substrate, is recovered and circulated to be reused. The coating solution is sometimes circulated in such a circulating type coating apparatus for a long time of 24 hours or more.
In the production of the electrophotosensitive material, a wide variety of electrophotosensitive materials are produced by using the same coating apparatus. During the production of the other kind of electrophotosensitive material, the coating solution must be stored for several days.
Therefore, the storage stability of the coating solution is insufficient in stable storage only for 24 hours and it is necessary to further improve the storage stability.